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New findings on the effects of xylitol ingestion in dogs

Once thought to cause only hypoglycemia in dogs, this sugar substitute has recently been discovered to also produce acute, possibly life-threatening liver disease and coagulopathy. And the number of reported exposures to xylitol has been increasing.

Xylitol is a sugar alcohol used as a sweetener in many products, including sugar-free gum and mints, nicotine gum, chewable vitamins, oral-care products, and baked goods. It can be purchased in a granulated form for baking and as a sweetener for cereals and beverages. Xylitol is a popular sweetener in Europe (especially Finland, Norway, and Russia) and Japan, and its use as a sweetener in the United States has grown rapidly over the last few years.

While xylitol consumption is considered safe in people, dogs can develop serious, even life-threatening, signs from xylitol ingestion. Xylitol's ability to cause hypoglycemia in dogs has been recognized for almost 40 years, but a recent study has found that xylitol also can cause acute hepatic necrosis.

XYLITOL'S HISTORY AND EFFECTS IN PEOPLE

Xylitol was first identified by the German chemist Emil Fisher in 1891; he produced it by hydrogenating D-xylose (wood sugar).1 It also exists naturally in many edible plants and fungi, such as berries, lettuce, and mushrooms,2 and is a metabolite in carbohydrate metabolism as an intermediary during the conversion of L-xylulose to D-xylulose.

Despite being identified in the late 1800s, xylitol was not used commercially until almost half a century later. During World War II, Finland began to produce xylitol because sucrose was unavailable. The process involved extracting xylan (a polysaccharide derived from hardwoods such as birch), hydrolyzing the xylan to its monosaccharide units (D-xylose), and then hydrogenating the D-xylose to produce xylitol. After the war ended and sucrose was again available, xylitol production was curtailed. Commercial interest in xylitol reawakened in the mid-1970s when large-scale xylitol production became practical. Now more efficient and economical techniques to produce xylitol, such as using corncobs left over from ethanol production, are being developed.2

Xylitol's growing popularity is based on its many beneficial properties. It is as sweet as sucrose on a measure-for-measure basis but has only two-thirds the calories of sugars. Because it causes little insulin release in people, it is considered a good sugar substitute for those on a low-carbohydrate diet and those concerned with the glycemic index of foods.2 Since xylitol doesn't require insulin to enter cells, it can be used as both an oral and intravenous energy source for diabetics; it is also antiketogenic.3 Experimentally, it increases bone calcification in aged rats; however, the significance of this finding in people has not yet been determined.1,2 Finally, xylitol has been shown to inhibit the growth of certain bacteria, which makes it useful in preventing bacterial otitis media in children.1,2 It also has anticariogenic properties because it prevents oral bacteria from producing the acids that damage tooth surfaces.1,2 For this last reason, it is increasingly being included in sugar-free gum, toothpaste, and other oral-care products.

METABOLISM

Oral absorption of xylitol varies greatly among species. In people and rats, xylitol is absorbed slowly (which increases the risk of osmotic diarrhea associated with excess sugar-alcohol ingestion); between 49% and 95% of oral xylitol is absorbed by people.4,5 In dogs, xylitol is rapidly and almost completely absorbed, with peak plasma concentrations occurring at about 30 minutes.6

In rats, most xylitol metabolism occurs in the liver. It is rapidly converted to D-xylulose, which is then metabolized via the pentose-phosphate pathway to glucose, glycogen, and, to a lesser extent, lactate.7 Virtually no xylitol is excreted in the urine.8

TOXICITY AND CLINICAL SIGNS

Oral xylitol has a wide margin of safety in most species. The oral LD50 in mice for xylitol is > 20 g/kg.8 In people, consuming > 130 g/day of xylitol will cause diarrhea but no other abnormalities.9 But it's a different story in dogs.